Left panel: average normalised error Δz_norm = (z_phot − z_spec)/(1 + z_spec) as a function of the magnitude r and the spectroscopic redshift z_spec. Right panel: redshift error z_phot − z_spec as a function of the spectroscopic redshift z_spec for galaxies with 18 <  r <  20 (orange dots) and 20 <  r <  21 (black dots). Each dot represents an individual galaxy (only 10% of the galaxies are shown, for better visualisation). The thick solid and dotted lines represent the median and the 68% confidence regions, respectively, computed in small z_spec intervals for the galaxies with 18 <  r <  20 (blue lines) and 20 <  r <  21 (red lines). The green line shows z_phot = z_spec. The results in both panels were obtained with a 100-fold cross-validation strategy on 𝒯₅.